Process for dehydrogenation of hydrocarbons



Patented Jan. 16, 1945 PROCESS FOR DEHYDROGENATION OF HYDROCARBONS Walter A. Schulze, John C. Hillyer, and Harry E.

Drennan,

Bartlesville, kla.,

assignors to Phillips Petroleum Company, a corporation of Delaware Application September 27, 1941, Serial No. 412,637 8 Claims. (01'. 260-680) This invention relates to the catalyticdehydrogenation of hydrocarbons to produce diolefins. It relates more specifically to an improved process for the dehydrogenation of olefins'to produce diolefins and has particular application to the production of low-boiling aliphatic diolefins from the corresponding olefins.

In the preparation of the valuable aliphatic diolefins by catalytic dehydrogenation of olefins without alteration of the carbon structure, one

-of the primary considerations has heretofore special treatment of the mixtures by means such as solvent extraction, super-fractionation or the like.

The presence of the corresponding parafiin hydrocarbons in the olefin-diolefin conversion has been objectionable because the conversion has been non-selective. Thus, the conversion conditions which produce satisfactory yields of diolefins from olefins have heretofore caused undesirable destruction ofaccompan'ying paraflins of four or more carbon atoms. This destruction of the parafiins has resulted in various processing difiiculties such as short catalyst life due to car- The refractory C3 hydrocarbons or mixtures containing major proportions thereof may also be used with suitable processing steps for separation and recycling. However, as noted above, higher paraflln hydrocarbons than C3 such as butane, pentanes, and hexanes, have not been suitable for inclusion in the olefin charge Stock because they have undergone conversion and/or decomposition in prior dehydrogenation processes. Thus'the paraflin hydrocarbons which almost invariably occur with the desirable olefin feed stocks and which are extremely diflicult to separate therefrom have been regarded as undesirable components of the dehydrogenation feed stocks.

It isan object of this invention to provide a process whereby the catalytic dehydrogenation of low-boiling aliphatic olefins to produce the corresponding diolefins is selectively effected in the presence of substantial amounts of the corresponding parafiin hydrocarbons.

It is a further object of this invention to provide a dehydrogenation process for the production of low-boiling aliphatic diolefins in which extensive segregation and/or purification of the olefin charge stocks to remove the corresponding paraffins is eliminated.

' presence of the corresponding parafilns to the bon formation, and lowered yields due to excess hydrogen production, not to mention the material losses to relatively worthless products.

Another important factor in the dehydrogenae tion of olefins to produce the corresponding diolefins is selection of a suitable diluent for addition to the olefin feed stocks. Because of the high conversion temperatures which are well into the range of thermal decomposition and the instability of the dioleflnic products, the olefin dehydrogenation is usually carried out with, low pa tial pressures of the olefin charge. The most sat sfactory expedient for obtaining low-partial pressures of olefins is the inclusion of a suitably inert diluent whereby olefin partial pressures may be adjusted to any desired fraction of the total system pressure. For this service various diluents have been suggested, including nitrogen, carbon dioxide, methane and the like.

extent that said paraflins are substantially un converted. I

We have found that in catalytic dehydrogenation reactions at dehydrogenating temperatures,

preferably in the range of 1100 to 1300 R, which alytic dehydrogenation of hydrocarbons has been generally condemned in the art because of deleterious effects on the activity of conventional dehydrogenation catalysts, and hence on con-- versions obtained over said catalysts. We have now found, however, that at the conditions of olefin dehydrogenation certain catalysts are either inherently resistant to poisoning by water vapor or may have water-resistant qualities induced by a chemical pre-treatment. This discovery of water-resistant catalysts together with the unexpected selectivity of olefin dehydrogenation in the presence of water vapor are the basis for the olefin dehydrogenation process of this invention. Our process make possible the dehydrogenation of stocks such as butene-butane mixtures or pentene-pentane mixtures with excellent yields of the corresponding diolefins wherein the paraffins are substantially inert diluents.

In one specific embodiment, our process comprises the steps of (1) diluting low-boiling aliphatic olefin stocks comprising C4 or heavier hydrocarbons with a considerable proportion of water vapor; (2)- treating the resultant hydrocarbon-water vapor mixture over a water-resistant catalyst to selectively dehydrogenate the olefins; and (3) separating the diolefin so produced from the unconverted hydrocarbons and other products.

The process may be illustrated by reference to the drawing in which Figure 1 is a flow diagram of one arrangement of conventional equipment for application of ourinvention to the dehydrogenation of low-boiling aliphatic olefins. Figure 2 is a flow diagram of an alternative manner of carrying out the dehydrogenation process described herein.

In Figure 1 the fresh, olefin-containing feed enters by line I and steam enters by line 2. The hydrocarbon-steam mixture passes through line 3 to heater 4 where it is heated to reaction temperature. The hot vapors then pass by line 5 to catalyst cases 6 containing a water-resistant dehydrogenation catalyst, and the treated vapors exit through line 1. The hot vapors passing through line I may be chilled by water injection through line 8, if desired, and pass to condenser 9 wherein water vapor is condensed and condensate removed through line I 0. The hydrocarbon vapors then pass through line H to diolefin separator l2, in which diolefins are extracted and removed through line l3. This may be effected by any one of several conventional methods such as chemical separation, solvent extraction, or the like.

The residual vapors pass through line H and leave the system through line I5. Provision is made to return all or a part of the hydrocarbon vapors of the proper boiling range to the system through line I6 for further conversion if desired. In such a case hydrogen and other light vapors could be removed from the recycle portion by means of fractionators, and/or other conventional arrangements of apparatus.

In an alternative procedure for carrying out the principles of this invention, provision may be made for obtaining essentially adiabatic reaction conditions in the catalyst chamber by the multipoint injection of steam diluent into different sections of the catalyst bed.

In the operation of this modified procedure, the steam may be superheated to or above reaction temperatures'in a separate furnace coil and injected into the catalyst bed to offset falling temperatures'due to endothermal heat of reaction As illustrated in the flow diagram of Figure 2, the parafiin-olefin charge is introduced through line 2| and is admixed with steam from line 22 prior to entering heating coil 23. The mixture is heated to reaction temperature, and passes through line 24 to catalyst cases 25. The concentration of pre-mixed steam from line 22 is points being selected to give the desired distri-- bution of steam. The eliluent vapors may be divided at the exit of the catalyst cases 25 with a portion being recycled to line 24 through line 30. The remainder passes through line 29 into which cooling water may be injected from line 3|, and

' thence through line 32, condenser 33 and line 34 to further processing from the recovery of butadiene as illustrated in Figure 1. The condensed water is withdrawn through line 35.

In the operation of our process, the charge stock is usually prepared in such proportions that the partial pressure of olefins is less than one atmosphere, and ordinarily in the range 0.1 to 0.5 atmosphere. The volume of water vapor added is from as low as 10.to as much as 90 or more per cent of the total mixed feed, but ordinarily in the range of from 25 to '75 per cent of the total, being regulated to maintain the partial pressure of olefin at the desired value. Thus in dehydrogenating a charge stock containing relatively little olefins together with a major proportion of the corresponding .paraffins, such as one having approximately the composition 30 to 40 volume per cent of n-butenes and to 70 per cent of n-butane, a volume of water vapor equivalent to only about one-third the volume of hydrocarbon need be used. On the other hand, in dehydrogenating a stream relatively rich in olefins under the same conditions, such as one containing about 70-75% butenes and only 25-30% butane, a volume of water vapor equal to twice the volume of hydrocarbon may be used, resulting in a partial pressure of butenes equivalent to the first case. These exemplary. volume ratios may be varied with specific operations on different low-boiling olefin-paraffin feed stocks and within the terms of our invention.

We prefer to operate our process at low pressures, at atmospheric to 100 pounds gage. Low total pressure is desirable to increase the yield ofdiolefin. Also, since the partial pressure of olefin is ordinarily kept below 0.5 atmosphere, it is desirable to operate at low total pressures in order to have maximum volume concentrations of this component. On the other hand, when low' concentrations of olefins are initially present in.

the charge and are still further diluted with steam, the size of equipment necessary to obtain a desired throughput of olefin may become excessive at atmospheric pressure. Individual conditions will guide the selection of a suitable operating pressure. I

To obtain satisfactory conversion of low-boiling aliphatic olefins to diolefins, temperatures in the range 1100 to 1300 F. are ordinarily employed. Flow rates used are between 1 and 10 liquid volumes of olefin charge per hour per volume of catalyst. In terms of the total vapor mixture charged to the catalyst, space velocities of 500 to 5000 are satisfactory under proper conditions. The particular combination of flow rate and temperature for a specific operation will depend on the catalyst employed, the composition of the charge, and on the degree of conversion desired.

By the terms water-resistant and/or wateractive as applied to the catalysts of this invention, we describe catalysts which are not poisoned by the presence of more than a trace of water vapor in the hydrocarbons undergoing treatment at the specified temperatures. Suitable catalysts have been determined by experimental selection or prepared by pre-treatment of suitable base materials. While not wishing to limit ourselves to any specific theory or reaction mechanism, it appears that the quality of water-resistance may be related in some manner to the hydroxide-oxide ratio or equilibrium on the surface of certain metal oxide catalysts as measured by the rate of desorption of water vapor by said catalysts. This complex equilibrium system may be a function of the natural properties of the catalytic materials, or it may be induced by treatment with certain metal hydroxides in a manner hereinaftrdescribed.

Of particular valueare catalysts prepared by the treatment of bauxite with the hydroxides or oxides of barium and/or strontium in such a manner that the adsorbent mineral ore is impregnated with minor proportions, usually from one to isfactory catalysts, we havefound certain other catalysts which possess the quality of water resistance to a marked degree. In general these catalysts comprise the diificultly reducible metal oxides of natural or synthetic origin which have been treated to produce water resistance, and especially said metal oxides when impregnated with relatively minor proportions of certain alkaline earth hydroxides or oxides.

The oxides of aluminum and magnesium have been found to give especially satisfactory'catalysts, as have also those of zirconium and titanium. Both synthetic preparations of the substantially pure oxides, hydrated oxides, or hydroxides, and also natural mineral ores comprising these oxides, can yield satisfactory catalysts. High porosity, or specific surface, and other qualifications of good catalysts are desirable in these materials, both before and after treatment to impart waterresistant qualities. We have found that various alkaline materials added to these untreated catalysts in such a manner as to impregnate the catalyst thoroughly, serve to impart the qualities of water-resistance and selective olefin dehydrogenation to a varying degree. While catalysts can be prepared by impregnating with alkali oxides, we have found the specific alkaline earth oxides and/or hydroxides of barium and strontium to be most satisfactory.

In the catalytic dehydrogenation over the above-described catalysts certain other benefits have been noted from the use of water vapor as a diluent. A prolonged period of maximum catalyst activity for olefin dehydrogenation is obtained when the preferred conditions are maintained. These benefits apparently are due to the use of water vapor in conjunction with the water-resistant qualities of our preferred catalysts, and to the function of ,the water vapor in reducing polymerization reactions and coke and/or tar deposithe water vapor is denoted in part by a more or less constant formation of carbon oxides in the eflluent vapors from the catalyst. Further, the water vapor may be cheaply provided in any desired amount and may be separated from the hydrocarbons by simple condensation; thus eliminating much of the compression and fractionation equipment necessary when other diluents are employed.

The increased yields obtainable by our process are also attributable to the presence of water vapor and to selective dehydrogenation. In addition to reduced cracking and polymerization reactions during dehydrogenation, hydrogen formation due to parafiin conversion and to coke deposition is drastically reduced with the result that substantially equilibrium dehydrogenation is obtained. This is in contrast to non-selective dehydrogenation in which large amounts of hydrogen produced by paraffin conversion have suppressed dehydrogenation.

After passing over the water-resistant catalysts, the vapor effluents from the catalytic treatment arecooled to condense and separate water and any high-boiling polymers. The method of cooling mayberdesigned to provide an extremely rapid reduction of temperature, such as the introduction of a quenching medium. For this pur-' salts, solvent extraction, and other chemical methods. I desired. Substantially pure b-utadiene can be.

Fractionation may also be practiced if produced by any of these processes, and nearly complete recovery of butadiene from the residual vapors may be obtained if economically desirable.

Since dehydrogenation is an equilibrium reaction, a portion of the butene will always remain unconverted, the exact proportion depending upon the equilibrium concentrations at the temperature employed and how closely other conditions of flow rate, catalyst activity and the like allow the equilibrium to be approached. Obviously, further diolefins could be obtained from the unconverted olefins in the effluent vapors, if desired, by recycling all or any desired proportion of them. Normally, hydrogen and all or a part of the other' light gases present in the residual stream will be removed before recycling to avoid repressing the dehydrogenation. Numerous arrangements of conventional equipment may be used to accomplish this purpose.

The water-resistant catalysts prepared and/or selected by the methods described may be reactivated over long periods of use by treatment with oxidizing gases to burn out carbonaceous residues responsible for decreased activity. In this connection it has been noted that in the reactivation of our preferred water-resistant catalysts neither high temperatures during reactivation nor the Example I A C4 hydrocarbon fraction from a refinery cracking operation, which contained about '70 mol per cent of normal butenes and 30 mol per cent of normal butane, was diluted with water vapor to reduce the butene content to about 25 per cent. The mixture, as subsequently charged to the preheater, had approximately the following composition:

Volume per cent Butenes 25 Butane 11 Steam 64 The charge was heated to 1185" F. and passed over a water-resistant catalyst consisting of bauxite impregnated with 3 per cent by weight of barium hydroxide at a space velocity of 1200 volumes per hour and a catalyst case inlet pressure of 3 pounds gage. The efliuents were cooled by direct water injection and the steam was condensed and separated. v

Before processing to remove butadiene, a sample of the efiluent hydrocarbons was removed for analysis. The C4 hydrocarbon fraction represented a volume yield of about 88 per cent based on the total C4 hydrocarbon content of the charge. Based On the charge, the following quantities of C4 hydrocarbons were recovered:

Volume per cent Butadiene 12 Butenes 46 Butane 30 This represented approximately 35 percent per pass conversion of the butenes charged, and about 50% efliciency in the conversion to butadiene, with little or no conversion of n-butane. The effluent gas was submitted to chemical separation, whereby substantially all of the butadiene content was separated from the residual vapors.

Example II A C4 hydrocarbon fraction, obtained from the efiiuents from a polymerization unit, contained about 10 per cent of normal butenes and 90 per cent of normal butane. This charge was diluted with an equalvoiume of water vapor before charging to the preheater. The mixed charge had the following approximate composition:

Volume per cent Butenes 5 n-Butane 45 Steam I 50 Analysis showed the C4 hydrocarbon fraction of the eflluents to comprise about 94 per cent of the volume of hydrocarbons charged. Based on the charge, the following volumes of products were obtained.

Volume per cent This yield represents approximately 40 per cent conversion or the butene with 40 per cent efliciency in conversion to butadiene. Only about '4 per cent or the butane was converted under these rather severe conditions.

Example III Butadiene Buten Butane Example IV The butene-butane-steam charge of Example I was dehydrogenated over a catalyst comprising synthetic zirconium oxide impregnated with 5% by weight of barium hydroxide at a temperature of 1190 F., inlet pressure of 3 pounds gage and flow rate of 1100 volumes. In this operation per cent of the hydrocarbon charged was recovered as C4 hydrocarbons as follows:

Volume per cent Butadiene 10.0 Butylene 45.5

Butane 29.5

This represents a conversion of 35 of the butene and 42% efliciency in conversion to butadiene, while the normal butane was recovered substantially unconverted.

' Example V In still another experiment the mixed feed oi. Example I was dehydrogenated over a catalyst comprisin a porous titanium oxide impregnated with 5% barium hydroxide. At 1190 F. a flow rate of 1200 volumes per hour, the eilluents analysis showed 89.5% of the hydrocarbon charge recovered as C4 hydrocarbons as follows:

Volume per cent 10.5 49 30 The analysis shows 30% conversion of the butene charged with 50% efilciency in butadiene formation.

Butadiene Butylenes Butane Example VI A C4 fraction produced by the dehydrogenation of n-butane and containing about 30 volume per cent of butenes, 69 volume per cent n-butane and the balance C3 hydrocarbons, was mixed with recycled butenes from the treatment to be described and charged to a dehydrogenation catalyst consisting of bauxite impregnated with 5 weight per cent of barium hydroxide to produce butadiene. Steam was added to the charge vapors at the inlet of a pro-heating furnace to produce a charge of the following composition:

Volume per cent This charge left the preheater at 1185 F. and at the inlet to the catalyst chamber steam at 1200 F. was injected, in an amount equal to about volume per cent of the resulting total mixture. This addition ofiset a slight drop in temperature in the transfer line and permitted correspondingly lower temperature in the preheater to produce an initial reaction temperature of 1185" F. at the point of entry to the catalyst case. Without steam addition at this point, the catalyst inlet temperature was about 1180 F.

During the passage of the vapors through the catalyst, an additional volume of steam at 1200 F. was injected at several points in the catalyst bed. The volume added amounted to about '7 volume per cent of the resulting total vapor mixture. The exit temperature of the vapors was 1150 F. whereas without steam injection and at equivalent space velocity the exit temperature was 1140" F. The higher average temperature throughout the bed produced a higher conversion of butenes to butadiene, and the additional incremental dilution of the efiluents increased the recovery of the diolefin without adversely affecting the equilibrium in the olefin-diolefin conversion reaction.

After processing the vapors to segregate nbutane and a butenes-butadiene fraction, the latter fraction was treated for the recovery of butadiene by methods described generally herein. The butadiene yield was 55 volume per cent based on the butenes charged to the second dehydrogenation catalyst. Example VII Volume per cent Pentenes 25 Pentane 15 Steam 60 The charge was heated to 1150 F. and passed over a water resistant catalyst consisting of bauxite impregnated with three per cent by weight of barium hydroxide at a space velocity of 1300 volumes per hour and a catalyst case inlet pressure of three pounds gage. The effluents were cooled by direct water injection and the steam was condensed and separated.

Before processing to remove pentadienes, a sample of the effluent hydrocarbons was removed for analysis. The C5 hydrocarbon fraction represented a volume yield of about 86 per cent based on the total C5 hydrocarbon content of the charge.

Based on the charge the following quantities of hydrocarbons were recovered.

Volume per cent Pentadienes 11 Pentenes 36 Pentane 39 This represented approximately 40 per cent per pass conversion of the pentenes charged, and

about 45 per cent'efllciency in conversion to pen tadienes, with little or no conversion of pentane. Example VIII The mixed butene-butane stock used as feed in the operation of Example I was similarly diluted with water vapor and treated at 1190 F.

over a water resistant catalyst comprising the natural mineral brucite, activated by dehydration at 1225 F., at a space velocity of 1200 volumes per hour and an inlet pressure of three pounds gage. Analysis of the efliuents showed that 45 per cent conversion of the butene was obtained per pass with about 40 per cent efiiciency in the conversion tobutadiene. The normal butane in the charge was substantially unconverted. The conversion cycle was somewhat shorter with this catalyst than with the catalyst of Example I.

Example IX In still another experiment, the mixed butene-- butane stock used as feed in Example I was similarly diluted with water vapor and treated over a naturally water-resistant catalyst comprising bauxite, activated by dehydration at 1200 F. At a temperature of 1190 F., a space velocity of 1500 volumes per hour and an inlet pressure of three pounds gage, the analysis of the eflluents showed approximately 30 per cent per pass conversion of the butene with about per cent efficiency in the conversion to butadiene, with substantially no conversion of the butane in the charge.

In all these exemplary operations, paraflin conversion corresponded to a minor amount of thermal conversion and/ or decomposition, usually not exceeding 1 to 3 volume per cent of the paraffins in the charge.

The foregoing examples have served to illustrate specific applications of our invention, but since other modifications will be obvious and within the scope of our disclosure, they are not to be construed as limitations.

While the foregoing disclosure has been relatively specific to the treatment of C4 hydrocarbons for the production of butadiene, we have noted that equivalent results may be obtained from the application of our process to oleflns of five or six or more carbon atoms in the presence of corresponding parafiins.

We claim: I

1. A process for the production of diolefins of four to five carbon atoms per molecule from the corresponding olefins which comprises contacting said olefin with a water resistant catalyst consisting essentially of a difficultly reducible metal oxide having incorporated therewith a minor proportion of a compound selected from the group consisting of the oxides and hydroxides of barium and strontium, in the presence of steam and under conditions such that dehydrogenation of olefins to the diolefins is the principal reaction of the process.

2. A process for the production of butadiene from butenes which comprises contacting normal butene with a water resistant catalyst consisting essentially of a difiicultly reducible metal oxide and a minor proportion of a compound selected from the group consisting of the oxides and hydroxides of barium and strontium, in the presence of steam and under conditions such that dehydrogenation of butene to butadiene is the principal reaction of the process.

3. A process for the production of pentadiene from pentenes which comprises contacting normal pentene with a water resistant catalyst consisting essentially of a diflicultly reducible metal oxide and a minor proportion of a compound selected from the group consisting of the oxides and hydroxides of barium and strontium, in the presence of steam and under conditions such that dehydrogenation of pentene to pentadiene is the principal reaction of the process.

4. A process for the production of butadiene from butenes which comprises contacting normal butene with a water resistant catalyst consisting essentially of an aluminum oxide and a minor proportion of barium hydroxide, in the presence of steam and under conditions such that dehydrogenation of butene to butadiene is the principal reaction of the process.

5. A process for the production of butadiene from butenes which comprises contacting normal butene with a water resistant catalyst consisting essentially of a magnesium oxide and a minor proportion of barium hydroxide, in the presence or steam and under conditions such that dehydrogenation of butene to butadiene is the principal reaction of the process.

6. A process for the production of butadiene by selective dehydrogenation of butenes in the presence of butane which comprises admixing said butenes and butane with steam, and passing the resulting mixture at a pressure within the range of to 50 pounds per square inch gage into contact with a water resistant catalyst consisting essentially of bauxite. and a minor proportion of barium hydroxide in the presence of suflicient steam in excess of ten percent by volume to produce an olefin partial pressure of less than one atmosphere and under conditions such that dehydrogenation of butenes to butadiene is the principal reaction of the process.

'7. A process for the production ,of butadiene from butenes which comprises admixing steam with said butenes in amount sufiicient to produce partial pressure of butenes in the range of 0.1 to 0.5 atmosphere at a total pressure of about 3 pounds per, square inch gage, and passing the resulting mixture at a pressure of about 3 pounds per square inch gage into contact with a catalyst consisting essentially of alumina and a minor proportion of barium hydroxide under conditions such that dehydrogenatio of butenes to butadiene is the principal reaction of the process.

8. A process for the production of butadiene from butenes which comprises admixing steam with said butenes, passing the resulting mixture through a bed of water resistant catalyst consisting essentially of alumina and a minor proportion of barium hydroxide under conditions such that dehydrogenation of butenes to butadiene is the principal reaction of the process, and introducing additional steam into said mixture at a plurality of points spaced along the catalyst bed in the direction of flow of said mixture.

WALTER A. SCHULZE. JOHN C. HILLYER. HARRY E. BRENNAN. 

